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ALEXANDER  VON   HUMBOLDT.                129
"We must devote especial attention to this subject,,
—the isothermic lines,—because it plays a very im-
portant part in Humboldt's scientific life, and has
occupied hint much during his whole career as the
favourite "branch of his studies. In. the year 1817,
when he published his essay, " De la distribution de
la chaleur et des lignes isothernies/* in the third vo-
lume of the French journal, JkTemoires d*A.rcueil, he
had already paid great attention to the distribution
of heat over the earth., and had endeavoured to deter-
mine the direction and form of these isothermic lines
more accurately. He also gave a lecture ten
years subsequently, on the 3rd July, 1827, before a
public meeting of the Academy of Sciences, on the
chief causes of the varieties of temperature on the
globe, and in his Asiatic fragments, he communicated
his detailed investigations and increased experiences
upon the subject.
Alexander von Humboldt begins by treating of the
climatic condition of Asia, and herein entirely follows
the  impressions  of his accurate comprehensive geo-
graphical acquirements, and at the same time extends
the subject to the entire earth, and goes back to its
universal laws.     On this field many errors had to be
corrected, and science had to be raised to a new grade.
It was formerly believed that the coldness increasing
from Europe towards the east was caused by the ele-
vation of the groxind above the level of the sea, bxit
it has now been plainly proved by facts that this is
not the case, and that, on the contrary, one may travel
from the Brabantine heaths eastward, as far as the
Asiatic   steppes   on   the  western   declivities   of  the
Altai, a direct line of 80 degrees of longitude, with-
out crossing an. elevation of 1200 to 1SOO feet.    And
travelling in a higher latitude from the Brabantine
heaths to the  Asiatic steppes, one would cross only*
unbroken plains as far as above the 65th degree of
latitude, a distance of nearly half the earth's circum-
ference.    This  Humboldt perceived, and that there-
fore the climatic changes must have other causes than